Modification feature layer

After two months of field collection on a point layer about 200 points with attachments (photo), the person who collects data said she would like to change the Feature layer (ex: add fields, change the ordre of certain field, delete fields, add choice answers in the value field). My Feature layer is on Arcgis Online. For now, I export my layer in arcgis online in FGDB format, I downloaded it and I can not change anything, because Arc GIS desktop tells me that my license does not allow me to change anything. I have a basic license (that does not support attachments). How can I do differently to modify the layer without losing attachments? I also have a web mapping application with this feature layer that can do editing on a post office for the person making the collection when it is back in the office and must make changes and also have a web mapping application that allows viewing only for managers. I absolutely have to change this layer without losing all attachments !!!! VERY IMPORTANT Can you help me please?